This invention relates to a code image quality check apparatus adapted to check the quality of a code image printed and recorded as an optically readable image of a piece of information containing at least audio information, video information or digital data. This invention also relates to a code image reader for optically reading such a code image and restoring the original piece of information of the code image.
The assignee of the present invention already proposed a dot code system for using a code image that is adapted to be printed and recorded on a printing medium such as an a sheet of paper as optically readable image of a piece of information that may be audio information and an optical reader for manually scanning the printed dot code and optically reading it to restore and output the original audio information. This prior art invention is disclosed in EP 0,670,555 A1.
FIG. 1 of the accompanying drawing schematically illustrates the physical format to be used for a dot code 10 of the proposed dot code system. The dot code 10 comprises a plurality of blocks 12 arranged two-dimensionally on a side by side basis. Each block 12 comprises a data area 14, a pattern code 16, markers 18 and a block address 20. The data area 14 contains a number of white dots 22 and black dots 24 representing so many "0s" and "1s" that are assigned to each block of error correcting code data including information data that may be audio information. As a matter of fact white dots are not recorded because the printing medium is a white medium. The pattern code 16 is used to locate the reference point for detecting each of the dots 22, 24 in the data area 14. The markers 18 are black markers arranged at the four corners of the block 12 so that the pattern code 16 may be detected. The block address 20 is used to identify the block when a plurality of blocks are read as block images and contains an error detecting or error correcting code.
For a more detailed description of dot code 10, refer to the above cited EP 0,670,555 A1.
The dot code 10 having the above described physical format is then printed by means of a printing machine that may be selected from a variety of printing machines of different types and different systems under various different printing conditions that are defined in terms of various printing materials including paper and ink to be used for the printing and the mode of regulating and controlling the printing machine. Therefore, the printed dot code has to be of a stable and good quality so that it may be read reliably by a code image reader of a specified type under any harsh conditions. This is the reason why a dot code of the type under consideration has to be checked for its quality.
Meanwhile, known bar codes are normally checked for the quality of printing by observing the strengths, the widths and the intervals of the bars. Printing press machines and other printers for printing bar codes are normally equipped with a bar code checking apparatus of a type as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-77530 so that the quality of the printed bar code may be checked automatically.
While it may be desirable to check all the printed matters for quality, a sampling and checking system of extracting samples out of a given set of printed matters and checking them for the quality in order to reliably control the quality of all the printed matter is popularly known. This technique is advantageous in terms of cost when compared with the process of checking all printed matters on a one by one basis and hence also popularly used for printed matters carrying photographs therein in order to check the quality of the photographs. In the case of a sheet-feed press for offset printing, the printing operation normally proceeds at a rate of about 10,000 sheets per hour. The quality of the printed photographs in the printed sheets is checked either by picking up sample sheets and examining only part of the photographs on the sheets or by measuring the density of a predetermined pattern formed by scattered elements on the margins of the sampled sheets by means of a densitometer. In either case, sample sheets are extracted from the entire printed sheets and examined only partly to determine the quality of all the printed sheets. This quality check technique is feasible because, in ordinary printing, the quality of the printed photographs would not significantly vary by every several sheets.
Thus, it will be a good idea to combine the above-described bar code checking system and the sampling technique and apply them to a dot code checking system. Then, the values (density, size and dot interval) characterizing the dots and the markers of the dot code carried on a sampled sheet will be measured to determine the quality of all the dot codes printed on all the sheets of paper to be examined for quality.
However, for applying the technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-77530 to dot codes, there is required an image analyzing apparatus comprising an image pick-up section and an image analyzing section for analyzing the contour and the density of the dots and other components of the image data sent from the image pick-up section. Then, the image pick-up section is required to pick up the image of an entire code with a level of resolution that allows the image analyzing section to analyze the profiles of the dots of the code. Such an apparatus will inevitably be bulky and costly. Additionally, since a dot code typically comprises a large number of dots and markers, it will take too much time for an ordinary image analyzing apparatus to analyze the profile and the density of the dots and the markers. Therefore, the use of an ordinary image analyzing apparatus for the examination of the quality of dot codes will be unrealistic.
Since a dot code 10 as shown in FIG. 1 comprises error correcting code data as information data to be printed and recorded, an error state display apparatus for digital data signals as disclosed in Jpn. Pat. Appln. KOKOKU Publication No. 63-33748 may alternatively be used for checking the quality of such dot codes. The disclosed error state display apparatus is designed to display the number or errors that have not been corrected as a result of an error correcting processing operation. Such an error state display apparatus eliminates the use of a bulky image pick-up apparatus as discussed above and hence can reduce the cost of dot code quality check operation.
However, there arises another problem that makes it very difficult to use such an apparatus for dot code quality check operations. The error correcting code data to be printed and recorded including information data are indispensably required to have the error correcting ability adapted to dot code read errors that are attributable to at least the quality of the dot code being read, the performance of the read apparatus and/or the undefinable reading conditions given rise to by manual scanning operation. Therefore, the error correcting ability of the error correcting code data including information data is such that no error will be left after the error correcting operation conducted during the operation of reading a dot code under normal reading conditions. However, it is impossible for an error state display apparatus as disclosed in Jpn. Pat. Appln. KOKOKU Publication No. 63-33748 to display the number of errors if it is used for a dot code quality check operation and hence is not suitably adapted to such an operation. Note that, for the purpose of the invention, "printing and recording" refers to not only normal offset printing and letterpress printing but also thermal transfer recording, ink-jet recording and other recording.
As described above, a code image to be read by manual scanning is provided with the ability to correct errors more than satisfactorily.
This will be discussed further by referring to FIGS. 2A through 3C.
FIG. 2A is a graph showing the relationship between scanning operation and code image read errors, where the scanning operation is manually conducted in an undefinable manner. Read errors increase as the scanning operation becomes not good due to an inclined, floating and/or rolling code image reader and/or a too high or low scanning rate. The hatched area 26 in FIG. 2A covers normal scanning operations that are typically conducted by ordinary users. P1 in FIG. 2A denotes the point corresponding to the worst scanning operation on the part of the user. In other words, most users perform better than the worst scanning operation. Note that the code image reader is a given apparatus operating as reference for scanning operation and the code image is a give image to be used as reference for quality check.
FIG. 2B is a graph showing the relationship between the performance of code image readers and code image read errors. Read errors increase. as the performance of the code image reader falls. The hatched area 28 in FIG. 2B shows the service provided to the user by code image readers. P2 in FIG. 2B denotes the point corresponding to the code image reader that operates as reference or the worst performing code image reader that can provide service to the user. The scanning operation of the code image reader at this point is the worst scanning operation conducted by the user and the code image is the one that operates as reference for a given quality check.
FIG. 2C is a graph showing the relationship between the quality of code image and code image read errors. Read errors increase as the quality of code image falls. The hatched area 30 in FIG. 2C shows the service provided to the user by code images. P3 in FIG. 2C denotes the point corresponding to the code image that operates as reference. The code image at this point is the code image of the worst quality that can be provided to the user. The code image reader used at this point corresponds to the one that operates as reference for the user and the scanning operation conducted by the user corresponds to the worst scanning operation.
FIG. 3A is a schematic illustration showing the relationship among the quality of code image, the performance of the code image reader and the fashion of manual scanning. The cuboid 32 shown in FIG. 3A is defined by the lengths of three edges directed perpendicularly relative to each other, or the length of a first edge representing the quality of the code image, that of a second edge representing the performance of the code image reader and that of a third edge representing the fashion of manual scanning. Assuming that the cuboid 32 is a cubic measure, then the volume of water 34 that can be contained in the cubic measure represents the number of code image read errors that will occur in the operation of reading a dot code image.
FIGS. 3B and 3C are illustrations showing the relationship between the originally provided error correcting ability and the code image read errors, supposing the scanning operation is manually conducted. The originally provided error correcting ability is represented by the volume of the cup 36 shown in FIG. 3B and that of the cup 38 shown in FIG. 3C. In FIG. 3B, reference numeral 40 denotes the read errors when the code image is checked by the best scanning operation of the code image reader and reference numeral 42 denotes the read error increment that arises when the code image is checked by the worst scanning operation of the code image reader. Reference symbols 40A, 40B and 40C respectively denote the read errors attributable to the code image reader, those attributable to the code image to be checked, and those that occur by the best scanning operation of the code image reader.
The cup 36 of FIG. 3B has a volume greater than the measure (cuboid 32) of FIG. 3A. Therefore, when the water 34 in the measure is poured into the cup 36, no water would flow out from the cup 36. This means that the originally provided error correcting ability has a margin for accommodating the difference 42 of between the errors of the worst scanning operation and that of the best scanning operation. Thus, in most cases, no water would flow out of the cup to signify that the number of errors left after the error correcting operation will be equal to "0" and the code image reader can substantially exactly reproduce the original error correcting code data.
It will be apparent from the above description that an error state display apparatus disclosed in Jpn. Pat. Appln. KOKOKU Publication No. 63-33748 and adapted to display the number of errors that could not be corrected by an error correcting operation cannot be applied to a code image quality check operation to be achieved by the present invention.
On the other hand, the cup 38 of FIG. 3C has a volume smaller than the measure (cuboid 32) of FIG. 3A. Therefore, when the water 34 in the measure is poured into the cup 38, water would eventually flow out from the cup 38. This means that the originally provided error correcting ability does not have any margin for accommodating the difference 42 of between the errors of the worst scanning operation and that of the best scanning operation. Thus, the original error correcting code data would not be reproduced exactly. It will be appreciated that an error state display apparatus disclosed in Jpn. Pat. Appln. KOKOKU Publication No. 63-33748 is designed to measure the amount of water that has flow out of the cup 38 and is adapted to check the quality of a code image reader or a code image recording medium by measuring the amount of water 46 contained in the cup 44.
As discussed above, the code image read errors that occur when a code image is read by a code image reader are generally defined in terms of the quality of the code image, the performance of the code image reader and the fashion of manual scanning, of which the fashion of manual scanning is dependent on the user and hence out of control of the manufacturer. Therefore, there is required a code image check method for reliably controlling the quality of a code image and the performance of a code image reader in order to allow the user to reliably scan an code image with a predetermined level of freedom of operation.
The term code image read error as used herein refers to the difference between an original error correcting code data to be correctly printed and recorded and the corresponding error correcting code data including information data obtained by printing and optical reading.